Artificial dental crowns and bridges are usually made today using a metallic framework coated with a fused dental porcelain to provide the desired aesthetics. A number of new non-metallic materials are now appearing on the commercial market which are made of mixtures of ceramics, and which are recommended for use in making artificial dental crowns and, in some case, bridges. These materials have coefficients of thermal expansion such lower than existing dental alloys, for instance, 5-8.times.10.sup.-6 versus 13-14.times.10.sup.-6, per degree Celsius. Therefore, existing commercially available dental porcelain glazes cannot be used on the non-metallic copings to provide aesthetic properties since the thermal coefficients of expansion are too high.
This invention describes a new family of dental procelains with lower thermal expansion values than commercial dental porcelain glazes, and therefore they match the expansion of the new ceramic copings. The new procelains have the property of being easily modified by minor changes of composition to allow the thermal expansion properties to be changed, in order to match various copings. They also have the desirable property of being stable after repeated firings, in that their coefficients of thermal expansion and color shades remain essentially constant. This is particularly desirable in those cases wherein the glaze will have to be fired more than once. Such instances include those wherein several layers of glaze are used in order to obtain special effects (e.g., a different shade at the tip of the restoration than at the gingival area), and multi-unit bridges. It is another useful property of the glazes of the invention that their maturing temperatures can be modified by minor compositional changes. This is desirable, for instance, in cases wherein several layers of glaze are used so that each successive layer matures at a slightly lower temperature.